The present invention relates to histamine H3 receptor antagonists, and as such are useful in the treatment of disorders responsive to the inactivation of histamine H3 receptors, such as obesity, cognitive disorders, attention deficient disorders and the like.
The histamine H3 receptor (H3R) is a presynaptic autoreceptor and heteroreceptor found in the peripheral and central nervous system and regulates the release of histamine and other neurotransmitters, such as serotonin and acetylcholine. The histamine H3 receptor is relatively neuron specific and inhibits the release of a number of monamines, including histamine. Selective antagonism of the histamine H3 receptor raises brain histamine levels and inhibits such activities as food consumption while minimizing non-specific peripheral consequences. Antagonists of the histamine H3 receptor increase synthesis and release of cerebral histamine and other monoamines. By this mechanism, they induce a prolonged wakefulness, improved cognitive function, reduction in food intake and normalization of vestibular reflexes. Accordingly, the histamine H3 receptor is an important target for new therapeutics in Alzheimer disease, mood and attention adjustments, cognitive deficiencies, obesity, dizziness, schizophrenia, epilepsy, sleeping disorders, narcolepsy and motion sickness.
The majority of histamine H3 receptor antagonists to date resemble histamine in possessing an imidazole ring generally substituted in the 4(5) position (Ganellin et al., Ars Pharmaceutica, 1995, 36:3, 455-468). A variety of patents and patent applications directed to antagonists and agonists having such structures include EP 197840, EP 494010, WO 97/29092, WO 96/38141, and WO96/38142. These imidazole-containing compounds have the disadvantage of poor blood-brain barrier penetration, interaction with cytochrome P-450 proteins, and hepatic and ocular toxicities.
Non-imidazole neuroactive compounds such as beta histamines (Arrang, Eur. J. Pharm. 1985, 111:72-84) demonstrated some histamine H3 receptor activity but with poor potency. EP 978512 published Mar. 1, 2000 discloses non-imidazole aryloxy alkylamines discloses histamine H3 receptor antagonists but does not disclose the affinity, if any, of these antagonists for recently identified histamine receptor GPRv53, described below. EP 0982300A2 (pub. Mar. 1, 2000) discloses non-imidazole alkyamines as histamine HS receptor ligand which are similar to the subject invention by having a phenoxy core structure although the subject invention is unique in the dissimilar substitutions at the ortho, meta or para positions of the central benzene ring, the exact substitutions of the non-oxygen benzene ring substituent, and in some cases the presence of a saturated, fused heterocyclic ring appended to the central benzene core. Furthermore the compounds of this invention are highly selective for the H3 receptor (vs. other histamine receptors), and possess remarkable drug disposition properties (pharmacokinetics).
Histamine mediates its activity via four receptor subtypes, H1R, H2R, H3R and a newly identified receptor designated GPRv53 [(Oda T., et al., J. Biol. Chem. 275 (47): 36781-6 (2000)]. Although relatively selective ligands have been developed for H1R, H2R and H3R, few specific ligands have been developed that can distinguish H3R from GPRv53. GPRv53 is a widely distributed receptor found at high levels in human leukocytes. Activation or inhibition of this receptor could result in undesirable side effects when targeting antagonism of the H3R receptor. Furthermore, the identification of this new receptor has fundamentally changed histamine biology and must be considered in the development of histamine H3 receptor antagonists.
Because of the unresolved deficiencies of the compounds described above, there is a continuing need for improved methods and compositions to treat disorders associated with histamine H3 receptors.
The present invention provides compounds that are useful as histamine H3 receptor antagonists. In another aspect, the present invention provides compounds that are useful as selective antagonists of the histamine H3 receptor but have little or no binding affinity of GPRv53. In yet another aspect, the present invention provides pharmaceutical compositions comprising antagonists of the histamine H3 receptor.
In yet another aspect, the present invention provides compounds, pharmaceutical compositions, and methods useful in the treatment of obesity, cognitive disorders, attention deficient disorders and other disorders associated with histamine H3 receptor.